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How do the orientation of spars and ribs affect the aerodynamic efficiency of wing?
There are various ways the ribs and spars can be oriented in the swept wing. Do the placement of ribs and spars affect the aerodynamics? And, what are the structural advantages of both orientations shown in the figure below? Why the ribs in the B737 wing are placed in both ways both parallel to the airflow and perpendicular to the spar?

Clearly it's going to depend on whether the skin is thick enough that the position of the wing ribs has no effect on the surface contour-- for an extreme case, consider a fabric-covered aircraft (or model airplane covered in Monocote etc...)

Comparing several cutaways I've noticed that all of the Douglas aircraft have had the same orientation like in the DC10 while all of the oldest Boeing have had the same orientation like in the B737. So I suppose that there was some kind of "structural company philosophy" behind those choices. Anyway starting with the 747 the orientation in Boeing has changed like in the Douglas models, so maybe that is actually better... or Boeing employed Douglas engineers :-)

It seems a better query would be how the orientation of spars and ribs affect everything else that needs to go in the wing.  The wing itself is designed to handle certain loads with out excessive deformation or flutter.  Essentially, aerodynamics would only be significantly affected if the structure were failing.  The B737 and DC-10 both flew successfully, this question may not.

The aerodynamics impose structural loads on the wing, and the structural loads impact aerodynamics!
It is really a complex interaction of various factors. In theory you design a wing to fulfil an aerodynamic purpose for the aircraft, such as subsonic flight, transonic flight, altitudes, etc, etc...
So you go and design your wing so it works aerodynamically.That's when loads arise such lift, drag, and bending moment whose distribution can be chosen and affected by

airfoil placement, sizing, and type.
control surface placement, sizing, and type
lift augmentation devices (such as flaps, spoilers, slats)

On aircraft like the DC-10, you have swept back wings for transonic flight. Each airfoil section causes lift and bending and torsion at differing points. Usually the center of lift of each airfoil is located along a line basically parallel to the leading edge, so the bending moments act around that line. So you could locate the spars parallel to that to handle the bending moment, and ribs perpendicular to that to take the torsion. On the 737 apparently they just did that for the tip because the root is likely subject to loads in a different angles. That's it, you're just gonna optimize the structure to the load direction.
The thing is that these aerodynamic loads are real and affect materials and cause deflections! So you have to build the wing structurally so that it will keep its shape while subject to those loads, otherwise you deviate from your plan!
Then you come and install accessories that also affect the wing loads. This includes:

engines and powerplants that produce thrust cause bending due to weight and cause vibrations
potentially propellers that alter the flow around the wing and cause perturbations and vibrations,
antennas that create drag and depending on the airflow can cause vibrations
landing gear that create drag and add weight, and cause bending, also vibrations
other special accessories such as pods, fairings, etc...

Oh and don't forget the usually large weight of the wing and all these things! Usually you are trying to minimize these the weight as much as possible, while still allowing decent safety margins.
These loads cause deformations, that need to be accounted for in your structural and aerodynamic calculations! So then you need to account for that as well... And you have to account for these effects in different phases of flights, for different orientations, different environments, and failure scenarios.
As you can see designing a wing is very complex!

Yes the placement of the ribs and spars affects the aerodynamics. How? This is an aeroelastic effect, what we call a fluid structure interaction (FSI). We ALL agree that there is a pressure difference above and below a wing resulting in a load upwards, but then there are perturbations due to the air, winds, turbulence, windshear etc. This means that the air pressure is constantly changing, and hence so is the loading. Changes to the wing structure can help tune the stiffness and rigidity of the wing to ensure it does not start to resonate with any aerodynamically induced flutter.
Also note that there are other loads, the drag force backwards, as well as induced loads for the use of control surfaces. This makes the change in orientation of the B737 design very sensible to account for the increased twist at the wing tip. I appear to be repeating this too much, I promise I am not sponsored by them, but check the FAA manual for more info [[1]].
[1] FAA. (2018). Aviation Maintenance Technician Handbook—Airframe Volume 1 (Chapter 1). Federal Aviation Admenstration.


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Which one produces more lift?
I have come across this question on Twitter. I have found a similar question here. The aircraft isn't flying but just doing Cobra Maneuver. Since the direction of the lift is in the same direction and the weight is the same, can I conclude the lift in both cases will also be the same given that it isn't climbing?

From one of the answers ( https://aviation.stackexchange.com/a/56476/34686 ) to the related ASE question cited in your question-- " For the purposes of the answer, we'll assume that Thrust acts parallel to the flight path through the airmass, although this clearly not always exactly true. This simplifying assumption leads to the following vector diagram:..."  Obviously that assumption would be extremely invalid for the "Cobra" maneuver!  You need to take into consideration the part of the Thrust vector that is acting perpendicular to the flight path.

(Ctd) That is not normally considered part of the Lift vector.  And that should give you the answer.

Is the top aircraft in equilibrium, or climbing?  (The cobra maneuver is dynamic, but the picture is just a snapshot in time.)

@MichaelHall Its in equilibrium

OK, so the red arrows must counter the weight as you point out, and they will be equal.  In the Cobra more of that comes from the engine thrust, but I trust you realize that...

@Auberron, The top aircraft is generally not in equilibrium,. When the cobra is performed, as Angle of Attack (AOA) increases, the aircraft lift is increased dramatically, until it reaches, and then exceeds, the critical AOA. But because the maneuver overshoots the critical AOA it places the aircraft AOA on the lift curve to the right of the critical AOA, where the Cl may actually be close to or equal to the Cl at a much lower AOA. The coefficient of drag (Cd) of course is much higher. But this is momentary, as the aircraft unloads back to a normal AOA again.

...can I conclude the lift in both cases will also be the same given that it isn't climbing?

No you cannot. If the aeroplane is not climbing in both instances, it means the vertical forces are in balance. But with a horizontal flight path and the nose tilted way up, thrust contributes to the upwards vertical force - therefore the wing lift must be lower.
Note that even though the nose is lifted up, lift is still vertically upwards if the flight path is horizontal, the plane is just flying with a large angle of attack.

Can you differentiate the case between the plane climbing up and not climbing at all? In which case lift will be smaller?

Direction of the lift vector is defined as being perpendicular to the flight path. So in a climb the lift vector is tilted backwards, reducing the vertical force compensating for gravity. Thrust will have to have a larger contribution in a climb - lift in a climb will be smaller.

This question is a favorite on the internet threads and forums, which can be easily resolved after a review of technical terms.
According to the NASA Glenn research center Lift is a force the acts perpendicular  to the free stream, not the heading, of the aircraft.
This presents a very interesting quandary to our understanding of "lift" in that by the NASA definition, any force component acting in this manner can be considered to be lift.
From that point of view, "lift" of both aircraft can be considered equal.
However, the contribution of the thrust vector to this stalled yet still flying manuever, in opposition to gravity, leads to a better understanding of forces involved with the level flight (or climb) of the "Cobra" aircraft.

Care to provide a link re the second paragraph?  It would surprise me if they were defining the lift vector as the sum of all forces that act perpendicular to the free stream, including any such component from the motor/ engine.  I.e. any such component in what we would normally call the "thrust" vector.  But, you never know, I've been surprised before, could be an example either of sloppy writing (e.g. not making clear they were addressing a simplified case where thrustline is assumed to be parallel to flight path), or could be an unusual alternative definition.

There it is, could not resist the perpendicular to "freestream" definition point of view.

I'd say that's some arguably sloppy writing in that source-- no real basis for saying "Lift is the force that directly opposes the weight of an airplane " unless they clarify they are speaking of level flight-- yes they certainly do state that lift  is "directed perpendicular to the flow direction"-- but I'd say that the caption in red in the upper left corner tends to suggest that they are not including any component of (what would normally call) the thrust vector which acts perpendicular to the flow direction.

(Ctd) Anyway the intent of the page is not completely clear but I don't think it really should be cited to support the idea that a component in the thrust vector acting perpendicular to the free stream should be "counted" as part of the lift vector.

@quietflyer Well, the argument in favor of our cherished ASE beliefs is the subsequent definition of lift as the interaction of a (wing) with a fluid.  Therefor, thrust does not count as lift.  It is just that the level aircraft presented a new twist to this old question.

Now, applying that to helicopters gets interesting.

Typical confusion resulting from using terms that have multiple definitions, with multiple conflicting assumptions, based on multiple different contexts/scenarios. Before we can start discussing something, we should decide amongst ourselves what the context/scenario is, and what we wish the terms to actually mean. Lift is especially vulnerable to mis-definition/confusion. Remember, ALL definitions are nothing more than arbitrary definitions, made to suit the problem/context we are working in. Defining Lift as the force opposing weight is useless for an inverted aircraft.

@CharlesBretana good comment but ... if the plane is inverted,  is the wing (functionally)?  But 100% agree on consistent definitions.  This one is a little fun, and with vectored thrust, perhaps way better flown unstalled with thrust doing most of the "lifting" and forward propulsion, like a helicopter.  A bit of a tease, would a fan jet be producing lift?

@Robert,  As you have probably garnered from my numerous posts on this topic, to me, Lift is just an arbitrary definition of some defined component of the TOTAL aerodynamic forces generated by the collision of fluid particles with the surface of an airfoil. We decide which component and which sections of the total airfoil to include, in order to suit the problem space we are attempting to analyze and work in.  But as to a Fanjet, are you referencing the engine? like as opposed to a TurboJet?

I think the first and most basic, definition of Lift should be that Lift (if we are attempting to distinguish it from Drag, is that component of the TOTAL aerodynamic force which lies perpendicular to the free-stream airflow passing over the airfoil. Then the two components (Lift and Drag) will align with the frame of reference of the aircraft's motion through the fluid, and therefore Drag will affect only the magnitude of the Velocity, and Lift will only affect the Direction (angle) of the velocity. This makes the DEs easier to work with.

"This question is a favorite..."  I beg to differ!  It certainly isn't my favorite.  :)

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What does the sound and flashing button indicate during this landing?
What does the sound in this YouTube video indicate? It is accompanied by a flashing button.
Does that sound indicate the touchdown of both the main and nose landing gear? The pilot also pressed the same button at the end of the video.

It's the "Master Caution" indication. The sound also belongs to this.
It tells you that something is not working by the books and that you should check it out immediately.
There was probably another indication lit as well giving more details about what is going wrong. But since the screens are covered (and I'm not experienced enough to tell from what's going on in the video) I don't know what exact issue occurred.
However, you see the First Officer taking care of it. Either he fixed it or decided that it was a no-issue so he presses the "Master Caution" button to turn the warning off.

Do you happen to know the resources that consists of different sounds aircraft produces like this?

@Auberron The sound are described in the CRJ manual - CHAPTER 2 - AURAL/VISUAL INDICATING AND RECORDING.

When Cautions come up like that on short final you just kill the MC and carry on the landing.

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Why aren't thermal analysis of propeller done?
I have searched for articles on Thermal Analysis of Propeller but couldn't find one. Can I assume the aircraft company don't perform heat transfer simulation and analysis of high speed propeller? Isn't that important? What kind of simulation can be done of propeller besides the flow simulation of propeller obtaining drag, thrust and efficiency of it? Thank you.

Why would you think one should do a thermal analysis of a propeller?

Propellers aren't "high speed", once the blade tips hit the sound barrier things don't work out very well, and that's pretty easy to do even with small diameter propellers...

"What kind of simulation can be done of propeller besides the flow simulation of propeller obtaining drag, thrust and efficiency of it?" This is a strangely open ended-question. Are you looking for a thesis topic or something? If that's what you're after, then structural analysis or aeroelasticity is one.

@DKNguyen Yea i am thinking the same.

@Auberron you are "thinking the same"... what? Please [edit] your question to include all relevant details.

As a propeller turns through the air at subsonic speeds, the dynamics of creating the pressure distributions in the air surrounding the propeller blade can be accurately modeled as being isothermal (no significant and persistent temperature gradients are created) and adiabatic (no significant net heat transfer from one location to another occurs within the flow field).
This means that the thermodynamic state of the air coming into the propeller disc is almost exactly the same as its state when exiting it, and for this reason there is no significant thermodynamic analysis needed to successfully account for the behavior of a propeller as long as it is subsonic.

Adiabatic and isothermal are mutually exclusive. I think you mean adiabatic in the thermodynamic sense (when calculating the compressibility of air), and isothermal in the sense that you don't take into account temperature dependency on the gas properties?

you are probably right.


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Is there any plane that has wing of both aerodynamic and geometric twist?
For the proper lift distribution, afaik either of the twist are used? Is there any significant difference having one over another and both? Thank you. The above question has one line answer and both questions can be merged into one.

Can you say how you think geometric and aerodynamic twists differ? I never heard of one without also doing the other.

A wing has geometric twist when, from root to tip, its chord line changes angle, typically without changing the airfoil shape.  This is colloquially known as washout when the root stalls before the tip (or, much more rarely, its opposite, wash-in).
A wing has aerodynamic twist when, from root to tip, its airfoil changes in camber and thus in shape, typically without changing its chord line's angle.
Both twists have a similar effect, in that the zero lift axis changes angle from root to tip, commonly to inhibit tip stalling.
Of these two, geometric twist is easier to design, construct, and analyze, because there's only one airfoil instead of a (possibly continuous) blend of multiple airfoils.
Adding geometric twist to aerodynamic twist might, for example, let you avoid a nonconvex airfoil shape where the camber is large.  Convex shapes are easier to build strongly and stiffly, so that would lighten the wing.


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Why don't we simulate similarity parameters simultaneously in the same wind tunnel?
As 'Fundamentals of Aerodynamics' by JD Anderson suggest

Today, for the most part, we do not attempt to simulate all the
parameters simultaneously; rather, Mach number simulation is achieved
in one wind tunnel, and Reynolds number simulation in another tunnel.

Is it done for accuracy? Or Does it need an extra big wind tunnel to do that?

It would be great if we could match all parameters at once. But that would require a tunnel large enough to accommodate the full size airplane and powerful enough to match the actual flight speed. The reality is that we cannot in most cases.
We have some answers here on windtunnel testing. They should cover the basics:

How are wind tunnels used with scale models?
What are some specific benefits of cryogenic wind tunnels?
How is windspeed scaled in wind-tunnel tests?

The most important similarity numbers are the Reynolds number and the Mach number. Both grow linearly with flow speed, so it helps to match flow speed. In case of the Reynolds number, the other parts of it are the length of the flow path and the viscosity of the fluid. If we use air, which is plentiful and free, we also need to match the actual size so that the Reynolds number matches the original. The Mach number also depends on the speed of sound in the fluid, which in turn depends on temperature.
It is possible to match both Reynolds and Mach number in super cold tunnels using a pressurised gas like nitrogen. This lowers the required gas speed so the tunnel needs less power to run and produces realistic results with smaller models. The expense of building and operating such a tunnel is immense, though.

It is extremely expensive to build a wind tunnel that can be both pressurized and handle high-velocity flow.
Such large-section wind tunnels do exist, but to maintain high pressure during a test run they require enormous pressure tanks which take ~hours to pump up to the required pressure, which can then be maintained for only ~seconds during a full blowdown run.
Digital simulation has gotten so accurate and fast that in some cases, wind tunnel tests of scale models are no longer strictly necessary for routine aircraft design tasks.


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Has anyone tried to make an aircraft using centripetal force to hover or fly or is it not going to happen
.        Air craft testing  might be the idea we need

Pretty sure that's an "edited" video.

This question is very unclear and the attached unattributed image isn't obviously related to the title.

Welcome to Stack Exchange! Can you explain what you mean by "using centripetal force to hover or fly"? There's no obvious way that centripetal force could be used to make something hover or fly, so the question doesn't really make sense.

Related to this post by any chance? https://aviation.stackexchange.com/questions/65513/is-there-any-developments-on-centrifugal-thrust

There have been various proposals at various times to try to use things like centripetal/centrifugal force, impact vs. rebound, and various other methods to extract a net force from the movement of mass.  All have failed, because momentum is conserved, and for the same reason, this method of propulsion will never work.


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What kind of propellers are generally mounted on the Aeriane Sirocco?
I'm curious what propeller is used for the Aeriana Sirocco. Online I see lots of pictures of propellers with three blades, but none with only two and I cannot find many clear pictures of the proppeler. Are there any Aeriana Sirocco aircraft flying around with (wooden) propellers with only two blades?

It's powered by a Rotax 447, and there are a ton of props you can use for that, mostly composites (carbon) and some wood, with or without reinforcement.

@JuanJimenez thank you a lot!

If this is the same aircraft as the Aviasud Sirocco then you can see lots of pictures in Google image search and many have a two-bladed prop.


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Muscle memory for weapons systems?
How often do military pilots train to retain muscle memory for use of weapons systems?

This is a broad question that has no real specific answer as there are no specific training sorties dedicated specifically to "muscle memory", let alone muscle memory specific to weapons switchology.
Military currency requirements exist for multiple functional skills, air to ground attack, air to air 1v1 ACM, Defensive ACM, carrier landings, instrument approaches, etc.  During any and all training events, whether in the aircraft or simulator, muscle memory is reinforced, but it is more of a by product of all the other things going on around it such as flying the aircraft, scanning the instruments, and executing the procedures.
These currency requirements are generally captured in some sort of a training matrix that is maintained by a squadron training officer, who communicates the requirements to the schedules officer.  Both of these individuals report to the squadron operations officer, who has overall responsibility for maintaining aircrew combat readiness.
Intervals between training simulator or flight sorties may vary by type aircraft, skill-set, and where the squadron is in their deployment/readiness cycle.  (i.e. just got back from war, or getting ready to head out?)
The closest thing to what you are asking is what we referred to as "blind fold cockpit checks".  Early in simulator training the instructor would have you close your eyes, then locate certain switches by feel, reinforcing muscle memory to both locate them and identify them by their often unique shape.
These drills, however, generally focused on switches related to emergency procedure memory items.  And more specifically, to items related to loss of electrical power, smoke and fumes in the cockpit, and other emergencies where vision could be impaired.


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What color are cockpit weapons control?
Forgive my ignorance in my wording of this question.
I assume the weapons control in a military aircraft cockpit are colored differently from other instruments the pilots has to look at considering U.S. military pilots are not allowed to be colorblind, Why do some Air Forces not allow Color Blind Pilots?
If that is correct, what color are the weapons controls?
Please add any appropriate tags I missed.

No pilots are allowed to be colorblind, it does not apply only to military pilots.

@J.Hougaard Colorblindness is not a either or proposition, there is a range of colorblindness.  Some people with mild colorblindness are allowed to be pilots.  That fact is recognized, §67.303 Eye. "Eye standards for a third-class airman medical certificate are:
(c) Ability to perceive those colors necessary for the safe performance of airman duties." https://ecfr.io/Title-14/pt14.2.67#se14.2.67_1303

Reasons for limiting colorblindness go way beyond military weapons system switches.  Lights of all sorts, both internal and external, are colored.

Depends what you define as a bonafide control? Lets look at the F/A-18C
Releasing a weapon from the aircraft is not just a case of pushing the red weapons release button or trigger. A MASTER ARM switch is included to prevent the accidental discharge of weapons, (and in some other aircraft countermeasures and stores jettison functionality). The MASTER ARM switch is not painted.
However this is still not enough, as the systems of the aircraft have to be programmed to release the selected weapon, perhaps by selecting the relevant weapon as configured in the STORES MFD page. In (most?) Hornet (blocks?), the MFD symbology is monochrome green regardless of the page selected.
There are shortcuts into weapons master modes though: The lowest hat switch on the stick is a shortcut into A/A master mode, with each direction selecting a different A/A weapon and the MFDs being changed to relevant pre-set pages. This switch is black, much like the other stick controls.
So, the pilot, colour-blind or not, has to be able to locate multiple controls in order to release anything from the aircraft, which are neither painted bright red, the same colour or any differentiating colour from their surroundings, except for the weapons release itself.
There are enhanced answers to be provided regarding workflows, muscle memory, the actual shape of the controls, training and the priorities of selection. There are much better qualified people here to talk about those.
P.S. I would provide an image to show where these controls are, but I'm not able to currently.

This gives me so much more than what I was asking for, and answers questions I didn't even think to ask.

… in a good way I hope?

Better than good.  I'm writing a novel and information including "lowest hat switch on the stick" and "the shape of the controls" are great details to add to the scene.

I'd definitely continue your research journey. I trust the information I've given you is accurate from a lay person's perspective, but I'm sure there are real pilots out there (including on here) who can give you the exact procedure (and stories) from their first-hand experience operating the aircraft you are trying to write about.

@Bob516 - not sure you're still interested, but the switch on the F-18 stick to select a weapon is called the "weapon select switch". Typically, once airborne pilots will select AIM-120 (by default) to enter A/A mode. From there, all that's required is to arm up the jet with the Master Arm switch and pull the trigger. For A/A weapons, pilots typically don't reference the 'stores' format, since selecting a type of weapon is accomplished by pushing the weapon select switch in one of four directions.


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How can the pilot tell the center engine failed on a piston aircraft with three engines?
There are a few aircraft, such as the Britten-Norman Trislander, that use three piston engines -- one on each wing and one mounted along the centerline somewhere.
This is fine and good, but how do you tell in a timely fashion that the #2 (centerline) engine has quit?  The engine gauges are in no hurry to tell you, as per Randy Sohn's Warbird Notes #6, and there's no adverse yaw because it's a centerline-mounted engine, but you still need to know and quick because unless you can get that prop feathered, there's a giant drag bucket hanging off your vertical tail!

Perhaps the giant drag bucket hanging off your vertical tail will be a clue?

Wouldn't the lack of adverse yaw be a sign by itself?

Another issue is that on two engine a/c you might see a MAP difference, but still be unable to tell which engine still produces power, and which is windmilling. Having 3 sets of instruments makes it easier to spot the "odd" one in relation to the remaining two engines still producing power

If the engine quits you will lose some thrust which will affect the plane's handling. You may even begin to descend slowly which the pilot will notice.
Most importantly you have engine instruments which will tell you, quite quickly, the engine has quit. If you have one, your manifold pressure will drop since you are no longer producing power, or your tach will reflect what is happening.
If all that fails you I would think there would be an audible difference if the engine cut out.
This is the cockpit of the aircraft in question:

(Image Source: Jetphotos.net)

It does show independent MAP and RPM gauges for each engine as opposed to some planes that have a single gauge with multiple hands (one for each engine). You would surely be able to see an altered reading on one of these gauges.

Interesting that you say that the engine instruments would pick up on it quickly -- is this a difference between radials and in-line/opposed reciprocating engines, or something to do with forced induction vs natural draft?

I would think that in cruise flight you would have your gauges set, if the engine cut out, even if the gauges still had a reading it would likely not be your set cruise power. As a pilot you chose your cruise settings and should check your instruments routinely. Granted MAP shows suction so if you chose your MAP to be equal to the atmosphere at that level you may not see a difference if the engine cuts as the MAP will measure ambient pressure.

MP is not a measure of "power produced" per se, but an indication of the pressure in the intake manifold. For a normally aspirated engine, with the engine running, MP will be below ambient pressure because of the engine working as a vacuum pump. With an engine failure, (considering a constant speed prop), RPM will at "best" remain constant, or more likely decrease with the governor unable to maintain the same RPM. This means less suction out of the manifold. Conclusion: MP will NOT decrease from an engine failure (normally aspirated, constant speed propeller). If anything, it will increase.

Which instrument will quickly tell you which engine quit? The propellers are constant-speed units, so RPM won't. And in normally-aspirated engines, manifold pressure is a function of ambient pressure, RPM and throttle position, so MP won't either since non of those three changed. And I don't see anything else in the picture.

Without having flown this particular aircraft:
According to Wikipedia, the aircraft is powered by the, non-turbocharged, Lycoming O-540-E4C5. This means that in a climb for instance, where you'd likely be at full throttle with this engine, if an engine stops (seizes), its indicated Manifold Pressure (MP) will be near ambient pressure, just like the other, running engines will be (at least for practical purposes), if it windmills, the engine will still work as a vacuum pump out of the throttle manifold, maintaining a still reasonable MP-setting. As the propeller will be windmilling initially, RPM is likely to, at least initially, stay in the same ballpark as the other engines (anyone who's flown older light piston aircraft will tell you most engine instruments are not accurate enough to make exact comparisons by value between the engines, try for instance syncing the propellers by the RPM gauge, and not by your ears). Unless the aircraft is equipped with torque indicators (not likely), the first instrument you will clearly be able to identify the engine failure is likely going to be the Exhaust Gas Temperature (EGT, an instrument I'm not sure if this aircraft is equipped with).
In a climb, or high powered cruise, the aerodynamic/kinesthetic feedback of the aircraft will be significant enough if you lose 1 of 3 engines, (deceleration, loss of climb performance, torque, change in sound) to warrant further investigation (and with proper training/experience, rather quickly conclude an engine failure). In a low powered descent, an engine failure can be quite insidious even on a light twin, and you are actually not likely to detect it until you apply power to level out.

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Which aircraft had such a luxurious-looking navigator's station?
I'm reading the BBC's How Fiji changed the way we travel; The little Pacific island nation was the first to incorporate GPS into its aviation system – and in doing so forever changed the way we get from Point A to distant Point B. and saw this photo of a spacious navigator's station with a large, elegantly designed desk, bay windows, and a small set of instruments.
What aircraft and timeframe was this? Does the photo portray a commercial flight?
bonus points: Were flare guns routinely stored out in the open like that at the time?

Until the late 20th Century, flight crews often included a flight navigator whose job it was to keep the plane on course (Credit: Museum of Flight Foundation/Getty Images)

Who else noticed the pistol in the bottom left corner? Uh, it's a flare gun .

@Bimpelrekkie the OP noticed it, it's a flare gun, that's why they asked about it as their bonus points question

On the bonus question: flares were often used for communication between planes, sometime even when all planes in the formation had radio (to the point that new flare systems had to be designed for high altitude pressurized bombers at the end of WWII). Given the number of cartridges right under the flare gun, I think it is indeed for communication and not just for distress signaling, so you would probably want it readily available.

@Luris tell us more! Did aircraft flying in formation ever use flares to communicate with each other?

That's not a bay window (and I haven't ever seen a bay window on a heavier-than-air craft).

@TobySpeight that's humor, as is the use of "luxurious" and "elegant".

Well the desk certainly does look luxurious and elegant, so your humour went straight over my head.  I guess sarcasm and facetiousness have never travelled well by 'Net...

@uhoh Sorry, I'm far from as knowledgeable on this subject than my comment could imply :) hence why I only made it a comment. The information I had was from this Forgotten Weapon  video about a pressurized plane's flare system, and what could be deduced from it.

It's a Boeing 314 flying boat. From the late 30s (look at the two rectangular windows behind the cockpit).
The last dedicated navigators on long range flights had started to disappear by the late 60s in the airline business.

Hmm, where is that? It looks like Lake Washington but I can't find clicking through the links.


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Why might an instructor in a small aircraft choose to descend with a substantial yaw on a first lesson?
Many years ago I took an introductory free (+fuel) flying lesson in a dual-control small aircraft (instructor in right seat) at a small city's municipal airport. There was a third passenger in the back. Near the end there was a report of a helicopter near the airport but there was some confusion as to the location.
When the instructor took us back down they did so in an unusual and exciting way, possibly to impress the third passenger, possibly trying to get back to the ground as quickly as possible because of the situation with the helicopter.
We were descending pitched substantially down, looking at the ground in the distance and with a startling amount of yaw with the right wing advanced by (estimate from memory) 20 degrees!
Is there a name for a descent like this? Are there standard reasons for it?

I don't want to dismiss your question but perhaps it was a completely normal maneuver. It might have seemed excessive at the time but from what you describe - "many years ago" and "from memory" - it's possible that it just felt more dramatic than it really was. For example, a forward slip is a standard technique, even if it might seem dramatic to passengers (and I probably wouldn't do it with non-pilots on board unless I needed to).

If there were a strong cross-wind, that would be the normal procedure for landing.

@RayButterworth there was no discussion of a cross-wind. There was extended discussion of "where is that helicopter?" I got the feeling that the instructor may have wanted to get down as soon as was practically possible.

@Pondlife I'm basing my perception of the "unusualness" on the reactions of the passenger and the interaction between them and the instructor not my own. I've been in small aircraft several times as a passenger with other pilots, sometimes in bad weather, but this was something remarkable. If forward slip is the answer to the question asked "Is there a name for a descent like this? Are there standard reasons for it?" then that's what I'm looking for as an answer "Slips are useful when you’re high and need to lose extra altitude in a hurry to make your touchdown spot." does seem to fit thanks

If not for a cross-wind, then perhaps using a standard glider technique for losing altitude quickly (without falling down).  The "Gimli Glider" was an extreme example of this, a Boeing 767 with dead engines, too close to an airport to land, and too close to the ground to circle around.

It's bad form to do forward slips to lose altitude on intro flights. Scares people.

Drifting comes to mind (probably not a proper answer) but if the instructor drives cars, perhaps he/she had a moment?

My instructor asked me if he could do a short-field takeoff on my discovery/intro flight. He then did a practice no-flap landing. Luckily, I had done air tours in pretty much every type of aircraft including an aerobatic glider by that time. Still not as stomach-turning as flying high speed nap-of-the-earth right before an airborne operation.

Sounds like a Forward Slip. It is not an unusual maneuver. It is very useful in order to descend faster than normal (Vertical Speed) without increasing your airspeed. The maneuver reduces the amount of lift generated while at the same time creating a large amount of drag by presenting the broad side of the fuselage to the relative wind.
Did the instructor happen to reduce the throttle to idle right before the maneuver?
It is also a great maneuver to practice in case a no-flap landing is needed due to flap failure.

A forward slip can provide very substantial descent rates with full flaps!

It can also give you better visibility ahead as you descend.


text:
What is it exactly about flying a Flyboard across the English channel that made Zapata's thighs burn?
CNN's French inventor makes 'beautiful' flight across Channel on hoverboard reports that:

"French inventor Franky Zapata has successfully crossed the Channel on a jet-powered hoverboard for the first time, after a failed attempt last month.

Later in the article it says:

The inventor said that he tried to "take pleasure in not thinking about the pain," even though "his thighs were burning."

What is it exactly about flying a Flyboard across the English channel that made Zapata's thighs burn? 20 minutes of standing shouldn't be that stressing, what is it exactly about flying this board that requires so much muscle activity that it would be painful?

Looks like you have never skied :)

What was his airspeed again? That's a lot of energy hitting your body.

@Mast Is Zapata European or African?

This is what he said after the 1st attempt

"When you fly with your body, even your hands affect the direction you want to go in. You feel the turbulence and the air through your fingers," Zapata told CNN.
  "It's like becoming a bird. But it's also very hard. I have to fight against the wind with my legs so there's pain too. It's not as peaceful as it looks."

https://www.cnn.com/travel/article/franky-zapata-flyboard-channel-gbr-intl/index.html
I imagine it's like a long ski run, where you're compressed down with every bump & turn.  Do a mile long run at high speeds and you really feel it in the thighs.

It sounds like he's both the pilot and the aircraft, facing dynamic structural loading

Indeed it does. Like a parachutist and wingsuit glider.

He's using the angle of his legs to control the attitude of the platform (and as a result, the direction he's flying in). So he can't take a relaxed pose, he's standing with his knees slightly bent the whole time.

I see, thanks! Hmm... I don't yet understand why it's necessary to have knees bent though. Most two-wheeled electric vehicles (e.g. Segway) let you move/drive forward and backward just by leaning a big, you don't need to bend your legs. I wonder what he's doing exactly that requires bent legs. Possibly because there is no road in this case, so no encoder...

@uhoh -- maybe because it lacks a vertical pole to hold on to, like the Segway has?

@quietflyer Since it's the inventor doing the flying, if it needed a vertical pole I'm sure he would have added it. I think it's more related to there being no contact with a fixed surface like the ground. Although... the pole wouldn't look cool, and Zapata does want to look cool, so maybe the burning thighs are the price one pays to fly without a handle.

@uhoh In an interview he mentioned that he's traveling at 160-170 km/h so simply resisting the wind takes a lot of effort.

@Sanchises I'll have to think about that. Presumably he's leaning into it a bit, so gravity will be helping, but I have no idea how much.

Even riding a Segway for an hour makes your legs start to ache, and that's much slower and more stable than this.

@uhoh - if it was set up to be balanced with knees straight, he'd only be able to tilt it backwards. I think it's designed for agility over comfort, which wasn't a problem when he only carries 10 minutes of fuel.

"he's standing with his knees slightly bent the whole time" It's like downhill rollerblading... try doing that for more than a few minutes lol

Have you tried an electric hoverboard - the segway without the control column? You steer it by off-balancing your feet. That is you lean forward. You have to then hold that position. If you stand up straight, you stop. I knew immediately what he meant.

There is another bit of information worth mentioning in the CNN link in CrossRoads' answer

The flyboard looks like a chunky skateboard and is powered by five
  small engines. It is fueled by kerosene, which Zapata carried 104
  pounds [47 kg] of in his backpack.

I believe that carrying a 50 kg backpack and balancing on a jet powered air skateboard combined delivers some serious strain on the pilot's legs.

And you really don't want to "hit the wall"


text:
Did the last US plane to leave Afghanistan have support from the control tower?
CNN's says says that

The last US military planes have left Afghanistan, Gen. Frank McKenzie, the commander of US Central Command, announced Monday at the Pentagon. The US departure marks the end of a fraught, chaotic and bloody exit from the United States' longest war.
"I'm here to announce the completion of our withdrawal from Afghanistan, and the end of the military mission to evacuate American citizens, third country nationals, and vulnerable Afghans," McKenzie told reporters. "The last C-17 lifted off from Hamid Karzai International Airport on August 30th, this afternoon, at 3:29 p.m. East Coast time, and the last manned aircraft is now clearing the airspace above Afghanistan."

Did the C-17 have help from the ground? Was the control tower still operational and provide clearance for takeoff and all other necessary services?

I cannot answer your question, but military operations such as this do not require/need any ground support at all.

Well, I wrote I can't answer, but turns out I did...

I got an alert from FlightRadar24 as the last flights departed Kabul. Among the aircraft leaving were several C17, a couple each of KC135 and KC10, a B-52, and, notably, an RC135. There may have been other aircraft not visible to FR24. I speculate that coordination for final departures was provided by the RC135.

"Clearance for takeoff" is not at all a "necessary service" for military aircraft in a scenario like this!

Information about Afganistan airspace is published online at www.afgais.com.
Last NOTAM published on OAKX (AFGANISTAN FIR) page reads as follows:

(G1264/21 NOTAMN
Q) OAKX/QAFAM/IV/NBO/E/000/999/
A) OAKX B) 2108160445 C) 2108180445 EST
E) KABUL AIRSPACE HAS BEEN RELEASED TO THE MILITARY. ADVISE TRANSIT AIRCRAFT TO REROUTE. ANY TRANSIT THROUGH KABUL AIRSPACE WILL BE UNCONTROLLED. SURROUNDING FIRS HAVE BEEN ADVISED.)

So, as of 2021-08-16 04:45 UTC [B)2108160445], the civilian air traffic services have not been available for the entire Kabul airspace. The NOTAM does give an estimate of this situation to end at 2021-08-18 04:45 UTC [C) 2108180445 EST], but since it was an estimate, and no new NOTAMs were released since, it must be assumed the situation has persisted.
There most certainly was some sort of ATC for Hamid Karzai International, but most likely this was provided by military personnel, and the last flight quite obviously took these controllers with them.
As the Taliban took over the control of the capital, effectively any judicial and executive entities related to former governing structures ceased to exist. Air traffic services were delivered under proxy from the former government, and thus could not be lawfully provided anymore (Chicago convention and international law may have something to say about this, but it's well outside my expertise). And, I bet the civilian controllers had other things to worry about aside the legal considerations of ATC services. Hence the surrendering the airspace to military. Interesting side question is, to which military...
Now, as for operating the last flight, it simply departed as any flight from an uncontrolled airport/airfield. These are not uncommon operations for military aviators, especially those at airlift duties. Flight coordination was most likely provided by an airborne control center. Overall it is imperative that any military operation is as redundant as possible, not requiring any kind of fixed or permanent units to maintain them.
Addendum: Many thanks for @uhoh for referring the following link to a news article describing the last phases of airlift operation from Kabul. It is for sure a condensed and somewhat dramatized version of how thing actually went, but essentially the last flights departed in a remotely coordinated manner with preplanned sequencing. The remote coordination was, as I previously mentioned, not necessary in any sense, so should there have been any lapse in communications, the departure would have proceeded as it did regardless of any thumb-upping or lack thereof.
CNN: Air Force commander details final hours before last US planes left Afghanistan
It must have been quite a sight having five C-17's execute a tactical takeoff within only three minutes.

This.. it was probably part of a larger operation which were directed by controllers aboard control-aircraft like Sentries or E-3 AWACS.

A comment here claims that the civilian contractors left relatively early and military controllers were working out of a tent on the field. And of course the Internet is always accurate.

I'm inclined to concur with that comment, as the civilians were most likely preoccupied with the safety of themselves and their families (?). Some kind of ATC service was absolutely necessary as the number of daily operations was quite high.

The Afghanistan FIR was uncontrolled so a free-for-all. OAKB was procedural and involved joining the stack and crews passing distances and other relevant info to the Tactical ATCers on the ground who were managing the running order.

News source indicating the airport is not running and they are reaching out to other countries to get the airport functioning again: https://www.aljazeera.com/economy/2021/8/31/taliban-in-talks-with-qatar-turkey-to-manage-kabul-airport

This may be worth considering adding, from CNN's Air Force commander details final hours before last US planes left Afghanistan "Pelbath also detailed the orders he gave when the final evacuation mission was set to be completed, saying that when he got the OK from Maj. Gen. Chris Donahue, the commander of the 82nd Airborne Division, he gave the order 'clamshell,' for the five planes to close up and begin taxiing the runway in Kabul.

"'Once all aircraft reported in to me that they were ready to go, Gen. Donahue gave me the thumbs up. We issued the 'flush the force' call and that was our indication for all of us to taxi together to the end of the runway,' Pelbath said. 'And then all five aircraft departed in a 30-second sequence, so we had all aircraft off the deck in under three minutes.'"

I'll check that out asap.

@Jpe61 I may post it as a supplementary answer then accept yours if you decide not to include this (or a better source for the same info) in your answer, but I think it's better if you can integrate this information into yours (if you so choose).

Been forgetting this... when I get on a proper device  I will integrate.

A few of the comments above have it completely right.
The tower was staffed by an ATC contract company (Serco I think) right up until the last few days. Once their manager pulled them out, a USAF Combat Control team working with a USMC ATC team provided tactical ATC until they boarded the last plane(s) out of there. Tactical ATC in this case means procedural control of aircraft (over-simplification, but akin to stacking them up) until they're within visual range.
The RC-135 (or AWACS/E-3s, etc) don't normally provide the kind of service that would be useful in a situation like that - although they may have been in this case. I honestly don't know about that part.
Obviously I can't provide a cite-able source, but this is via direct conversations with those involved and their supervision.


text:
How close to the White House did the Space Shuttle Discovery "fly"?
The CNN article For 747, transporting a shuttle is no heavy burden shows the shuttle Discovery on top of a "shuttle shuttle", a special 747 used to shuttle the space shuttles around.
How close to the White house did it fly? Did there need to be any special arrangements to fly so close to this highly sensitive airspace (especially post-9/11)?
Note: Presumably this is a NASA aircraft rather than a military aircraft (e.g. Marine 1) so the flight planning for this "fly-over" may not be exactly the same as those for landing a helicopter on the White House lawn.

Regardless of NASA or military, government owned and operated aircraft are generally exempt from the FARs.

According to this article they cruised through DC at an altitude of 1,500 Ft. Based on the pictures you can see here and here and here and lastly here of the flight and some of the locations it banked at its course seems to have taken it right around the prohibited flight area noted in Carlo's answer which you can see on the sectional here:

(source)
Foreflight does a better job of overlaying that on a street map. Assuming they kept a reasonable margin if we drop a ruler on it Im showing ~0.6 NM

(source: own images)
As for special clearance they were flying the the SFRA and would need to follow the rules on that as everyone else. Im sure the course was prearranged as the FAA prefers transitions more than loitering in the SFRA. The SCA also had a fair number of limits to its flight regime as discussed in this podacast the weather would have also needed to be optimal for the flight to occur.

@ymb1 that photo speaks directly to the question, it deserves to be in an answer, thanks!

@Dave thanks for taking the time to write such a detailed answer.

Based on the images, very close; regarding the restrictions and permission: flight around the National Mall, which includes the airspace over the White House lies under P-56, which is Prohibited Airspace. P-56 lies within the Flight Restricted Zone around DC which is surrounded by the District of Columbia Air Defense Identification Zone (ADIZ).
Flight in this area is restricted to anything except law enforcement or military activity, though rare exceptions can be made. In this case, I believe that was the final flight of the Shuttle Endeavour and the 747 SCA, which toured various cities throughout the United States. I’d say NASA could make the appropriate phone calls and get that flight approved only for that purpose.

So ... how close did they fly?

Imagine if the White House's SAM sites had gotten a little too eager that day


text:
What did Fiji have to do when it incorporated GPS into its aviation system?
I'm reading the BBC's How Fiji changed the way we travel; The little Pacific island nation was the first to incorporate GPS into its aviation system – and in doing so forever changed the way we get from Point A to distant Point B..
The article (and photos!) are quite interesting and worth a read. I'll quote just one paragraph below:

Fiji approached the US and its Federal Aviation Administration (FAA) to volunteer as the testing ground for GPS navigation. The FAA agreed to fund the upgrade, supplying equipment and technical support in return for the knowledge it could take away from the trial. It would take well over a year to get the system ready; in addition to the installation of the equipment, new flight routes had to be charted, manuals developed and pilots and crew trained.

and later:

Fiji proved that GPS could improve aviation in myriad ways, making it faster, more efficient and safer. In the quarter century since Fiji adopted GPS navigation for its domestic flights, the technology has been adopted around the globe, often with the direct help of Fiji’s new experts.

I'm having trouble understanding what exactly Fiji did when it "incorporate(d) GPS into its aviation system". Does this refer to installing GPS receivers on domestic Fiji Airways planes and training only, or were there any hardware or procedural changes on the ground as well?

I'm not sure if any other tags are appropriate...

Most of what it did was probably just develop the RNAV approach system in use today, including charting out approach courses, minimums, etc.

This early ICAO document covering the introduction of GNSS (GPS) should cover the whole topic quite well. I would skip to section 3 (page 75) Information on Fiji’s Early Application of GPS Technology. But the highlights are effectively:

Fiji consists of 300 islands (mostly volcanic) scattered over 200 000
  square miles of ocean. Of these, only 100 are inhabited. There are
  nineteen airfields, plus seven that are privately owned, but only five
  of the nineteen have NDBs and one has VOR-DME. This means that 80 per
  cent of the area is without any form of navigation aid. There are also
  helicopter and seaplane operations. Navigation has been accomplished
  primarily through visual flight rules or dead reckoning.
...
Fiji became involved in FANS and GPS in 1990/91 through briefings given by CAA Australia, and became
  convinced of the safety and cost benefits to be gained. Ad hoc trials, including long distance oceanic flights with a
  hand-held GPS receiver convinced Fiji of the potential of the GPS.
...
Under a Memorandum of Co-operation (MOC) the United States FAA provided equipment and operational and
  technical support to carry out trials and demonstrations. GPS receivers were provided for installation in all domestic
  IFR aircraft. These early receivers were not certified, and special procedures were developed to ensure that all the
  information provided by the GPS was confirmed by other navigation sources.
...
Some of the main features are listed here.
• GPS routes had been designed to all nineteen aerodromes. The GPS route charts show GPS airways and GPS
  way-points at the intersections.
• GPS checkpoints were established and surveyed on all the aerodromes, initially using a GPS receiver but
  now these have been resurveyed by an outside contractor to WGS-84.
• Outside areas of VOR/DME coverage, the pilot DR is now replaced by GPS procedures.
• Cloud break procedures were also designed to enable pilots to descend below cloud and make visual contact
  with the island, so that in most cases they leave a pilot at 1 000 ft above obstructions, five miles out, on the
  extended centre line. This information together with way-points were entered into the GPS receivers via data
  cards, by the CAA Fiji.
• Pilots and controllers were trained and examined on the rules and procedures. Pilots also had to undergo a
  practical test before being approved and pilots may not use the GPS unless they are approved.
• Based on this initial experience, the charts have been further simplified so that pilots can now select, on the
  GPS receiver, straight-in approach or cloud break, when this was needed.

This early 90's advertisement for Trimble GPS units also makes claims to being the ones that were used on these first approaches.
According to the document Fiji basically moved everything over to GPS; en-route navigation, approaches, the whole shebang. This helped them fly safer in IFR and have way more coverage than their limited ground based beacons gave them. The US helped not only create procedures, plates and information but also equipped all Fiji based operators and airfields.

Thanks for all the research! This was a quite a big project; I wonder if it's ever been written up in aviation journals.

I couldn't find any other articles on the Fiji GPS trial so I'l make an educated guess... What it means is the US provided equipment and training for Fiji Airways, and the Fiji regulating authority approved the installed equipment for primary navigation within Fiji airspace, and it also sounds like they may have created and approved some non-precision approaches at outlying airports, allowing them to be used as IFR destinations and alternates where Fiji couldn't afford traditional radio-based NDB, VOR, or Localiser based approaches (Wide Area Augmentation System GPS precision approaches came much later so you wouldn't have had GPS replacing ILS approaches during that trial).
The article has that written-by-a-wide-eyed-layperson-journalist quality to it and makes it sound like airlines got around over the oceans only by celestial navigation and dead reckoning before GPS.  The majors used Inertial Navigation, Omega, and Loran prior to GPS for oceanic navigation.    Not quite as precise as GPS today, but good enough at the time.  For a while, General Aviation had Loran C (Computerized Loran), quite popular in the 80s.

Thanks! As far as "...provided equipment..." would that pretty much be the GPS receivers and modifications to the aircraft, or would there have been any equipment modified on the ground? I can't think of any, just wondering.

Just airborne equipment.  There wouldn't have been any ground based equipment until the ground based augmentation equipment that enhances the GPS signals for precision approaches came along, in the early 2000s.


text:
How was the "frozen wing flap grease" problem solved? (Antarctica, 2001 emergency evac)
In the June 16, 2016 Washington Post news article A rare, risky mission is underway to rescue sick scientists from the South Pole difficulties of flying in and out of the south pole in winter are discussed. The article describes an earlier emergency evacuation in April of 2001:

The replacement doctor for the station disembarked, and the ailing Shemenski clambered onto the plane. But as they started up the engines, the crew realized they couldn't take off. The Twin Otter's skis had stuck to the ice beneath them, and the grease on the wing flaps had frozen them in the fully extended position. While the station workers hacked at the ice on the skis, the plane's mechanic jerry-rigged the controls to allow it to take off. It was one of the longest, slowest take-offs any of them had ever attempted, but eventually, they were in the air.

How did the jerry-rigging of the controls of the De Havilland Twin_Otter allow it to take off from the south pole in winter with its flaps fully extended because of the frozen wing flap grease?
Is there a better description of the problem and the actual solution that was implemented?
note 1: According to the article, the current rescue mission can be monitored at https://flightaware.com/live/flight/CGKBO
update: apparently this hasn't actually been the case.
note 2: The article also says there are actually two planes involved in the rescue mission.

Two small bush planes are flying to the South Pole this week to evacuate workers at the Amundsen-Scott research station — a feat rarely attempted during the middle of the Antarctic winter.

Flight tracker has no updates since June 15. Anyone knows a better source?

@AntonStrogonoff Seem there may be a delay due to weather. According to http://calgaryherald.com/news/local-news/calgarys-antarctic-rescue-mission-delayed-by-weather, "The two aircraft will continue to wait in Punta Arenas until they have a ‘favourable’ weather window, when they will fly to the research station in Rothera and once again wait for a weather window to make the flight to the research station and make the rescue." I've added a note to the question as well. Thanks!

@AntonStrogonoff update: One plane returning from South Pole to Rothera base (Antarctica) http://www.nsf.gov/news/news_summ.jsp?cntn_id=138999& and to Punta Arenas, Chile http://edition.cnn.com/2016/06/21/health/south-pole-medical-evacuation/...

This article makes it clear that one plane flew all the way to the South Pole, while the other waited at the Rothera base, ten hours' flight away, as emergency back-up.

@uhoh thanks for the heads-up. They pulled off one hell of a flight

Flying with the flaps extended is perfectly possible, just inefficient. At that point they were probably just trying to get in the air, not worrying about their fuel efficiency or airborne speed. Otters normally land and take off with flaps somewhat extended. The main problem is that with flaps fully extended, acceleration will be low, so it will be a long, slow takeoff. One issue is that if the plane has any icing, being in a full-flap condition can lead to a stall.
Once things get down to -50F or below, stuff really starts to freeze. For conditions like that you need to start replacing grease with graphite lubricants. Even fuel freezes so the planes have to use special heaters.
Here is a more technical description of the event by an electrician:

We then refilled the smudge pots and brought out tanks containing
  about 1,000 gallons of fuel to refuel the plane. They also brought out
  3 Herman-nelsons, portable diesel heaters used to warm up planes and
  other big equipment. At about 2:15AM, the plane was started but some
  of the hydraulics in the tail controlling the flaps were frozen. We
  called to get the Herman-nelsons back to heat up the flaps. They ran
  their engines the whole time, and we had to bring out another 100 or
  200 gallons of fuel.
Finally, at about 5:00 AM, the plane was working right and was ready
  to go. But then it appeared the plane was stuck in the snow. So a
  couple of guys stood on a car-like vehicle with tank treads, and shook
  the plane's wing. This caused the whole plane to rock back and forth.
  But finally the plane broke free and taxied to the skyway. The plane
  turned around and took off and flew in the -64F air.
Brother Aaron Coy, Local 48 Portland, OR Amundsen-Scott South Pole
  Station, South Pole, Antarctica

There are no hydraulics in the tail, obviously, so the electrician is confused about something. The hydraulic system in an ski-equipped Otter is used for the flaperons (in the wing) and for the ski controls.

Twin Otter at Casey Station

Maybe the hydraulics were jerry-rigged in the tail? Seriously though, any idea what "... jerry-rigged the controls to allow it to take off." could be referring to?

As far as ..."start replacing grease with graphite lubricants..." goes, it's not clear if the issue was really that Ken Borek Air used the "wrong kind of flap grease", to borrow a term from the Washington Post :)

At temperatures far below freezing icing is no issue. Air is so dry that there is hardly any water left which could be collected by the wing. The problem is the reduced range with flaps out.

@PeterKämpf The first paragraph in my answer was a discussion of the general considerations concerning flaps.  In any event, as it happens, icing is a serious problem in Antarctica because the aircraft has to be heated and the heating creates water which then refreezes. Also, airborne supercooled water droplets exist in Antarctica just like they do elsewhere and it is not unusual for flights to be cancelled or missions aborted due to unexpected icing conditions.

"Flying with the flaps extended is perfectly possible, just inefficient."

Not necessarily - some aircraft have flaps that deflect so far they are adding tons of drag and no more lift, essentially acting as speedbrakes.  It's quite possible you couldn't take off in such a condition.

"heating creates water" - do you mean there is pre-existing ice from supercooled water droplets during the flight to the south pole, and the heating of the flaps described in the quoted text may have melted some unseen ice that then refroze in such a way as to restrict the flap motion?

@uhoh Snow tends to accumulate on the plane due to wind and when you land snow gets kicked up. This snow later melts and refreezes when heaters are applied.

OK thanks! Do you think that the Washington Post description "... and the grease on the wing flaps had frozen them in the fully extended position." has the "grease" part wrong? If the article said the flaps were frozen, I wouldn't be so interested. But frozen wing flap grease ...?

@uhoh So far, no technical report has been issued, and, as a matter of fact, Antarctic missions have a notorious reputation for being deficient in filing detailed activity reports, even though the work is publicly funded.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Private Plane security United States 1975
in 1975 Famous Teamster Boss Jimmy Hoffa disappeared after being picked up at a local restaurant.
One of the theories is that men from New Jersey boarded a plane, landed in Detroit, and assisted with the disappearance.
Security for a private planes in modern day seems to range from lax to moderate to very strict, depending on the airport.
My question?
Considering, Airport employees, pilots, flight logs, records and other obstacles, just
how likely would it have been in 1975 that shadowy figures would be able to board a plane from New Jersey to Detroit undetected, without leaving something for Law enforcement to go on?
Thank you for the taking the time to read my question.

since the question is about aviation nearly 50 years ago, I've added the aviation-history tag.

I'm confused about by question.  You say "Security for a private planes in modern day seems to range from lax to moderate to very strict, depending on the airport."  As I see it, "security for private planes" relates to measures that would prevent people from tampering with, sabotaging, stealing components of, or stealing, etc, private planes.   What is this connection between this, and the ability of persons to fly on private planes without leaving behind a trail?  Are you asking specifically about security cameras that the police might be able to access afterwards, if they had a reason to?

Along the same lines, I can see an argument that the ability of people to freely travel by private plane without leaving behind a trail for others to follow, might represent an enhancement in security (at least for the security of those people), not a deficit in security.  I'm thinking along the lines of --celebrities, paparazzi, etc.

Quiet Flyer- all I was saying is that in some airports, people drive up and get on the plane- others require a security checkpoint- others seem to have the same procedure as commercial only without the line ups. It varies is all.

The following applies just as well today as it would have in 1975:
If the weather was clear...
Flight plans here in the US are only required for IFR flight. Radio communications are only required in controlled airspace and/or when necessary for IFR flight, and/or when operating out of a controlled airfield.
That being said, if the weather is above VFR minimums you could easily fly from an uncontrolled field in NJ to an uncontrolled field in and or around Detroit without ever even talking to anyone on the radio let alone filing a flight plan.
Airport security is a mixed bag depending on what your talking about and if you are going to include all ~16,000 Fields in the US (at last count) then the range is everything from nothing to "is that even a runway" up through a 2 foot fence with a sign that says "Pilots and Passengers Only" all the way up to full customs zones that allow intercontinental travel with TSA agents all over the place, metal detectors and loads of stuff you cant see.
There are plenty of small airfields (redish circles here, many of which have been around since the 70s) within a stones throw from NYC and Philadelphia all in NJ that would be prime candidates for such an operation. You could easily get a 1970's vintage twin prop plane in and out of most of these fields and cary out such a flight.
As for "logs and records" the onus to complete those is on the pilot and there are plenty of historic examples of such logs being omitted, forged, and/or manipulated for nefarious reasons. For VFR flights there is no legal paperwork required to get in the air, log books are generally filled out after the flight.

I think it's worth emphasising that this answer is just as applicable to 1975 as it is today.

Thank you for your detailed response Dave much appreciated!

Thank you Ben- this has been a hard answer to get from people.

"the range is everything from a 2 foot fence with a sign..."  I'd lower that to "nothing".

A quick search of weather history indicates it was good weather (70s/80s, no precipitation, good visibility) in Detroit and at least some parts of NJ on that day.

As there is no requirement to file flightplans for VFR flights in most places AND no requirement to file a list of occupants of a private aircraft, it's quite possible to fly from one place to another without the police knowing about it.
This was as true in 1975 as it is today, certainly in the USA.
Now, when talking with ATC you may be required to mention how many people are on board (we sure did when I was having flying lessons), but you don't have to tell anyone your names.
On a busy field nowadays there'd be cameras everywhere and recordings might exist for a while until the tapes are wiped to be reused. But unless there is a search warrant those tapes won't ever be handed over to the police except when voluntarily handed over when there is a known security breach.
Back in 1975 that'd have been far less likely as such equipment was far less common.
But even now, if you're at a quiet field, there may not be any cameras. I was in Canada at a small field in 2018 and there were not only no fences, but no cameras, and most buildings had locks that for anyone with even the simplest of tools could be removed in seconds (and anyone having an aircraft parked there would have keys anyway).
Some hangars had cameras on the inside, nothing on the outside however.

ATC will generally only as for the number of souls on board if you declare an emergency.

Thank you for your informative response Jwenting.

Back in 1975 that'd have been far less likely as such equipment was far less common. Closed Circuit TV monitoring was quite common by 1975. But recording was still very expensive until the 1980s, and therefore extremely unlikely at a small private field.

@manassehkatz-Moving2Codidact yes, and recording was also not really feasible for longer periods because of the massive bulk of the tapes you'd need. The first compact video tapes didn't come about until about a decade later, and those would only hold about half an hour to an hour.

@MichaelHall yes, though for airliner flights (especially international) there are additional reporting requirements for national security and law enforcement reasons. Those agencies like to know where people are, especially foreigners.

Of course, but the question was specific to private domestic flights.  And ATC doesn’t care about passenger manifests or customs declarations.  They will only ask for souls on board in an emergency.  I can’t speak to your flight training experience, but that sounds like an unusual exception.


text:
I'm having a hard time conceptualizing this statement from "The Jet Engine" by Rolls-Royce
This is taken from section 21 of Chapter 3, Compressors that discusses axial flow compressors in turbine jet engines.

The more the pressure ratio of a compressor is increased the more
difficult it becomes to ensure that it will operate efficiently over
the full speed range. This is because the requirement for the ratio of
inlet area to exit area, at the high speed case, results in an inlet
area that becomes progressively too large relative to the exit area as
the compressor speed and hence pressure ratio is reduced. The axial
velocity of the inlet air in the front stages thus becomes low
relative to the blade speed, this changes the incidence of the air
onto the blades and a condition is reached where the flow separates
and the compressor flow breaks down

I'm trying to draw a connection to something I already understand, is this similar to the phenomenon that limits propellers to low speed? In order to produce positive thrust they need to spin faster and faster?

https://www.wiley.com/en-it/The+Jet+Engine%2C+5th+Edition-p-9781119065999 (also here)

Related: What are variable stator vanes? and Does the stator blade angle changes? Why?

Variable pitch propellers can help explain this.
When the aircraft speed is slow, the blade pitch is finer.  At faster air speeds the blades must be opened more in the direction of the airstream.
This is due to the fact that the velocity of the airstream contributes to the relative wind on the propeller.  The rotational velocity of the prop is the other contributor.
If the propeller is opened but the airstream velocity drops, then the angle of attack of the relative wind on the prop will increase.  If the AoA gets too high, flow will begin to separate from the prop airfoil.
The compressor blades are all little airfoils.  They will behave exactly the same way if incoming airflow slows down too much.

Picture 3.9, which is related to the text you copied in your question, is helpful in understanding the concept:

First of all note that with "inlet" they mean the beginning of the axial compressor and not the inlet of the whole engine.
Now, going from the inlet toward the outlet, the section of the compressor becomes smaller and smaller: that's simply because air gets compressed and occupies a smaller and smaller volume. Obviously the outlet area cannot become indefinitely small: there are mechanical and aerodynamic limitations that cannot be overcome. That implies that if you want/need to add compression stages then you have to add them to the left, by the inlet section. But each section added to the left has a bigger and bigger area i.e. blade span. A bigger blade span is achieved both increasing its outer radius (Ro) and decreasing its inner radius (Ri). But higher radius means bigger rotating velocity while smaller radius means smaller rotating velocity, which are both bad since:

Higher rotating velocity at the tip means getting closer and closer to transonic or even supersonic speeds: drag and noise increase and lift decreases.
Lower rotating velocity at the base of the blade means lower Reynolds numbers and higher AoA to get enough lift despite the lower velocity: drag increases as well as the chance to get the blade stalled.


text:
What other times has a Chinese high-altitude balloon entered US airspace?
In an AP news article there's a quote from a politician stating:

“This is not the first time a Chinese balloon has entered American
airspace over sensitive national security areas,” Daines said in a
Friday statement to the AP. “I don’t think anyone believes this was
merely a civilian aircraft.”

Of course trying to google for these other events only turns up pages and pages of results about this latest incident in 2023 so I'm curious as to the other occasions mentioned in the quote.

different but related: To what extent is modern "maneuverable spy balloonery" really a thing?

In this season of the year every balloon released in the eastern/northern hemisphere that flies that high would end up in the US.

In WWII, the Japanese released a number of FuGo balloon bombs (https://en.m.wikipedia.org/wiki/Fu-Go_balloon_bomb) with high explosive devices attached (it was assumed), to attempt to start forest fires. Most landed in forested areas in the NW but did little damage.

this former CIA agent also mentions "there have been Chinese balloons that have flown over the United States in recent years" after about 04:50 https://youtu.be/RWn9L6x6qGA?t=290 and DW News mentions an earlier balloon during the previous administration https://youtu.be/kpD9LYP-41I?t=168

The largest part of UFOs seen by military are balloons. They are classified as UFO/UAP (unidentified aerial phenomena) since this is what they are until identified. According to the 2022 US report on UAP,  510 sightings were analyzed, to find 163 balloons. They can't be attributed to one state, nor can't be sorted by missions, unless shooting them down, with the associated consequences.

At this time this appears to be misinformation spread deliberately by the current administration. No evidence has been presented to support the assertion that this happened previously, and multiple high ranking officials from the previous administration deny the existence of prior balloon incursions.

I do not see why we should care what Trump or his national security advisors think about balloons.  If there was a Chinese balloon in US airspace, why would they even be told about it?  It's not an important event.  Spying happens all the time.